library: Implement properties based signing config

Signed-off-by: Harsh Shandilya <harsh@prjkt.io>

.gitignore

@@ -8,4 +8,7 @@
 gen
 
 .idea
-*.iml
+*.iml
+
+keystore.properties
+*.jks

library/build.gradle

@@ -1,5 +1,9 @@
 apply plugin: 'com.android.library'
 
+// Create a variable called keystorePropertiesFile, and initialize it to your
+// keystore.properties file, in the rootProject folder.
+final def keystorePropertiesFile = rootProject.file("keystore.properties")
+
 android {
     compileSdkVersion 27
 
@@ -11,10 +15,31 @@ android {
         consumerProguardFiles 'consumer-proguard-rules.pro'
     }
 
+    // If the keystore file exists
+    if (keystorePropertiesFile.exists()) {
+        // Initialize a new Properties() object called keystoreProperties.
+        final def keystoreProperties = new Properties()
+
+        // Load your keystore.properties file into the keystoreProperties object.
+        keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
+
+        signingConfigs {
+            release {
+                keyAlias keystoreProperties['keyAlias']
+                keyPassword keystoreProperties['keyPassword']
+                storeFile file(keystoreProperties['storeFile'])
+                storePassword keystoreProperties['storePassword']
+            }
+        }
+    }
+
     buildTypes {
         release {
             minifyEnabled false
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+            if (keystorePropertiesFile.exists()) {
+                signingConfig signingConfigs.release
+            }
         }
     }
 }